Study Details

Study Title: Investigating Safety Impact of Edge Line on Narrow Rural 2-lane Highways by Empirical Bayes Method

Authors: Sun et al.

Publication Date:JAN, 2014

Abstract: Narrow, rural two-lane highways are mostly characterized by low design features, light traffic volumes with high crash rates and particularly high fatal crash rates. There are about 5,000 miles of narrow, rural two-lane highways administrated by the Louisiana Department of Transportation and Development (LADOTD). Running-off-roadway (ROR) crashes are the most common type of crashes on narrow, rural two-lane highways. As it's not required by the Manual on Uniform Traffic Control Devices (MUTCD), many highways of this type do not have edge lines because of their low traffic volumes. There are two main concerns for edge line implementation on narrow two-lane highways: (1) the potential increase in head-on collisions and; (2) added maintenance cost to the already constrained annual maintenance budget. This paper introduces the second part of a study that evaluates the safety impact of edge lines on narrow, rural two-lane highways in Louisiana. The first part of the study proved that edge lines centralize the lateral position of vehicles based on the data collected from 10 locations. This second part of the edge line study evaluates the safety performance before and after the implementation of edge lines from roadway segments selected from all LADOTD districts. By using the Empirical Bayes (EB) method, the study shows that edge line implementation significantly reduces expected crash frequencies. While reducing ROR crashes, edge line implementation also reduces head-on crashes. It is interesting to note that the implementation of edge lines benefits primarily male drivers and young drivers. Because of the crash decreasing trend observed in the three year period that is classified as the after time period in the study, the final estimated crash modification factor (CMF) is 0.85 with a standard deviation of 0.039. The very high benefit-cost ratio strongly supports the idea of edge line implementation on narrow, rural two-lane highways in Louisiana.

Study Citation: Sun, X., D. Subasish, Z. Zhang, and F. Wang, Investigating Safety Impact of Edge Line on Narrow Rural 2-lane Highways by Empirical Bayes Method. Presented at thhe 94th Annual Meeting of the Transportation Research Board, Washington, D.C., (2014)

Related Citations: Sun, X., Das, S., "Safety Improvement from Edge Lines on Rural Two-Lane Highways," Louisiana Department of Transportation and Development, Report No. FHWA/LA.11/487, Baton Rouge, LA, (2011)

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Delineation

Countermeasure: Install edgeline pavement markings on narrow, rural, two-lane roads

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
0.85152 StarsAllAllNot specifiedRural